Solid-state image sensor, electronic apparatus, and control method of solid-state image sensor

ABSTRACT

To prevent the black dot phenomenon from occurring in a differential amplification-type solid-state image sensor. A signal-side amplifier transistor generates an output voltage corresponding to a signal current corresponding to one of a pair of differential input voltages by supplying the signal current from an output node to a common-phase node. A reference-side amplifier transistor supplies a reference current corresponding to the other one of the pair of differential input voltages to the common-phase node. A constant current source constantly controls a sum of the signal current and the reference current to be merged at the common-phase node. A bypass control unit connects the output node and the common-phase node and supplies the signal current having a value corresponding to a predetermined limit voltage to the common-phase node in a case in which the output voltage reaches the limit voltage.

CROSS-REFERENCE TO RELATED APPLIATIONS

This application claims the benefit under 35 U.S.C. § 371 as a U.S.National Stage Entry of International Application No. PCT/JP2017/007397,filed in the Japanese Patent Office as a Receiving Office on Feb. 27,2017, which claims priority to Japanese Patent Application NumberJP2016-081956, filed in the Japanese Patent Office on Apr. 15, 2016,each of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present technology relates to a solid-state image sensor, anelectronic apparatus, and a control method of the solid-state imagesensor. Specifically, the technology relates to a differentialamplification-type solid-state image sensor, an electronic apparatus,and a control method of the solid-state image sensor.

BACKGROUND ART

Solid-state image sensors which produce image data by photoelectricallyconverting light have been used in imaging devices since the past. Adifferential amplification-type image sensor that amplifies differentialsignals using a pair of transistors for the purpose of increasingsensitivity, for example, has been proposed (e.g., refer to PatentLiterature 1). Such a differential amplification-type solid-state imagesensor has unit pixels from which pixel signals are read and dummypixels from which no signals are read arranged therein. In addition, areadout circuit included in the solid-state image sensor reads pixelsignals differentially amplified by a differential pair formed by anamplifier transistor included in a unit pixel and an amplifiertransistor included in a dummy pixel and performs a correlated doublesampling (CDS) process thereon.

Here, the CDS process is a process of reducing fixed-pattern noise byreading signals from pixels twice and obtaining a difference betweenlevels of the signals as pixel data. The level of signals read the firsttime is called a P-phase level and the level of signals read the secondtime is called a D-phase level.

CITATION LIST Patent Literature

Patent Literature 1: JP 2008-271280A

DISCLOSURE OF INVENTION Technical Problem

In the above-described technology of the related art, the readoutcircuit outputs data of a difference between the P-phase level and theD-phase level as pixel data having a value corresponding to an amount ofexposure. With regard to the technology of the related art, however,there is concern of a black dot phenomenon occurring in a case in whichvery strong light is incident, in which pixel data of light approaches avalue close to “0” (a black level) in spite of the incidence of thelight. The reason for occurrence of the black dot phenomenon is that avery large amount of electric charges is generated in a photodiode dueto strong light and the electric charges may leak into a floatingdiffusion layer, which causes the P-phase level to increase and thusthere is substantially no difference between the P-phase level and theD-phase level.

In consideration of the above circumstances, the present technology aimsto prevent the black dot phenomenon from occurring in a differentialamplification-type solid-state image sensor.

Solution to Problem

The present technology has been made to solve the above problems, and afirst aspect thereof is a solid-state image sensor and a control methodthereof, the solid-state image sensor including: a signal-side amplifiertransistor configured to generate an output voltage corresponding to asignal current corresponding to one of a pair of differential inputvoltages by supplying the signal current from an output node to acommon-phase node; a reference-side amplifier transistor configured tosupply a reference current corresponding to the other one of the pair ofdifferential input voltages to the common-phase node; a constant currentsource configured to constantly control a sum of the signal current andthe reference current to be merged at the common-phase node; and abypass control unit configured to connect the output node and thecommon-phase node and supply the signal current having a valuecorresponding to a predetermined limit voltage to the common-phase nodein a case in which the output voltage reaches the limit voltage.Accordingly, an effect of connecting the output node and thecommon-phase node is exhibited in the case in which the output voltagereaches the predetermined limit voltage.

In addition, according to the first aspect, a signal processing unitconfigured to perform predetermined signal processing by reading asignal from an effective pixel circuit among the effective pixel circuitand a dummy pixel circuit may be included. The signal-side amplifiertransistor may be disposed in the effective pixel circuit, and thereference-side amplifier transistor may be disposed in the dummy pixelcircuit. Accordingly, an effect of connecting the output node and thecommon-phase node is exhibited in a case in which an output voltage ofthe effective pixel circuit reaches a predetermined limit voltage.

In addition, according to the first aspect, the dummy pixel circuit maybe shielded from light. Accordingly, an effect of connecting the outputnode and the common-phase node is exhibited in a case in which an outputvoltage of an effective pixel circuit not shielded from light reaches apredetermined limit voltage.

In addition, according to the first aspect, the dummy pixel circuit maynot be shielded from light and may be disposed in proximity to theeffective pixel circuit. Accordingly, an effect of connecting the outputnode and the common-phase node is exhibited in a case in which an outputvoltage of the effective pixel circuit in proximity to the dummy pixelcircuit reaches a predetermined limit voltage.

In addition, according to the first aspect, the bypass control unit mayinclude a bypass transistor having a source connected to the outputnode. Accordingly, an effect of connecting the output node and thecommon-phase node by the bypass transistor is exhibited.

In addition, according to the first aspect, the signal-side amplifiertransistor may output a P-phase level as the output voltage and thenoutput a D-phase level that is different from the P-phase level as theoutput voltage. The limit voltage may include a P-phase limit voltagethat limits the P-phase level and a D-phase limit voltage that limitsthe D-phase level. Accordingly, an effect of limiting the P-phase leveland the D-phase level is exhibited.

In addition, according to the first aspect, the bypass control unit mayfurther include first and second resistive elements connected to thebypass transistor in parallel. A gate and a drain of the bypasstransistor may be short-circuited. A resistance value of the firstresistive element may be a value corresponding to the P-phase limitvoltage, and a resistance value of the second resistive element may be avalue corresponding to the D-phase limit voltage. Accordingly, an effectof limiting a P-phase level and a D-phase level using limit voltagescorresponding to the resistance values of the first and second resistiveelements is exhibited.

In addition, according to the first aspect, the bypass transistor mayinclude first and second bypass transistors having different thresholdvoltages. Gates and drains of the first and second bypass transistorsmay be short-circuited. A threshold voltage of the first bypasstransistor may be a value corresponding to the P-phase limit voltage,and a threshold voltage of the second bypass transistor may be a valuecorresponding to the D-phase limit voltage. Accordingly, an effect oflimiting a P-phase level and a D-phase level using limit voltagescorresponding to the threshold voltages of the first and second bypasstransistors is exhibited.

In addition, according to the first aspect, the bypass control unit mayfurther include a selector configured to select one of a power sourcevoltage and first and second bias voltages that are different from eachother and supply the selected voltage to a gate of the bypasstransistor. The first bias voltage may be a value corresponding to theP-phase limit voltage, and the second bias voltage may be a valuecorresponding to the D-phase limit voltage. Accordingly, an effect oflimiting a P-phase level and a D-phase level using limit voltagescorresponding to the first and second bias voltages is exhibited.

In addition, a second aspect of the present technology is an electronicapparatus including: a signal-side amplifier transistor configured togenerate an output voltage corresponding to a signal currentcorresponding to one of a pair of differential input voltages bysupplying the signal current from an output node to a common-phase node;a reference-side amplifier transistor configured to supply a referencecurrent corresponding to the other one of the pair of differential inputvoltages to the common-phase node; a constant current source configuredto constantly control a sum of the signal current and the referencecurrent to be merged at the common-phase node; a bypass control unitconfigured to connect the output node and the common-phase node andsupply the signal current having a value corresponding to apredetermined limit voltage to the common-phase node in a case in whichthe output voltage reaches the limit voltage; and an image processingunit configured to perform predetermined image processing on image datagenerated from a signal of the output voltage. Accordingly, effects ofconnecting the output node and the common-phase node and performingimage processing are exhibited in the case in which the output voltagereaches the predetermined limit voltage.

Advantageous Effects of Invention

According to the present technology, a differential amplification-typesolid-state image sensor exhibits an excellent effect of prevention ofthe black dot phenomenon. Meanwhile, the effects described herein arenot necessarily limited and may be effects described in the presentdisclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example of a configuration ofan electronic apparatus according to a first embodiment of the presenttechnology.

FIG. 2 is a block diagram illustrating an example of a configuration ofa solid-state image sensor according to the first embodiment of thepresent technology.

FIG. 3 is a block diagram illustrating an example of a configuration ofa pixel array unit according to the first embodiment of the presenttechnology.

FIG. 4 is a circuit diagram illustrating an example of a configurationof a differential amplifier circuit according to the first embodiment ofthe present technology.

FIG. 5 is a block diagram illustrating an example of a configuration ofa column signal processing unit according to the first embodiment of thepresent technology.

FIG. 6 is a diagram illustrating an example of currents flowing in thedifferential amplifier circuit before limitation according to the firstembodiment of the present technology.

FIG. 7 is a diagram illustrating an example of currents flowing in thedifferential amplifier circuit after limitation according to the firstembodiment of the present technology.

FIG. 8 is a timing chart showing an example of a driving operation of apixel circuit according to the first embodiment of the presenttechnology.

FIG. 9 is a flowchart showing an example of an operation of thesolid-state image sensor according to the first embodiment of thepresent technology.

FIG. 10 is a circuit diagram illustrating an example of a configurationof a differential amplifier circuit according to a first modifiedexample of the first embodiment of the present technology.

FIG. 11 is a circuit diagram illustrating an example of a configurationof a differential amplifier circuit according to a second modifiedexample of the first embodiment of the present technology.

FIG. 12 is a timing chart showing an example of a driving operation of apixel circuit according to the second modified example of the firstembodiment of the present technology.

FIG. 13 is a block diagram illustrating an example of a configuration ofa solid-state image sensor according to a second embodiment of thepresent technology.

FIG. 14 is a block diagram illustrating an example of a configuration ofa pixel array unit according to the second embodiment of the presenttechnology.

FIG. 15 is a circuit diagram illustrating an example of a configurationof a differential amplifier circuit according to the second embodimentof the present technology.

FIG. 16 is a timing chart showing an example of a driving operation ofodd-row pixel circuits according to the second embodiment of the presenttechnology.

FIG. 17 is a timing chart showing an example of a driving operation ofeven-row pixel circuits according to the second embodiment of thepresent technology.

MODE(S) FOR CARRYING OUT THE INVENTION

Exemplary embodiments for implementing the present technology (whichwill be referred to as embodiments below) will be described below.Description will be provided in the following order.

-   1. First embodiment (example in which output node and common-phase    node are connected)-   2. Second embodiment (example in which output node and common-phase    node are connected by having effective pixel and dummy pixel in    proximity)    <1. First Embodiment>    [Example of Configuration of Electronic Apparatus]

FIG. 1 is a block diagram illustrating an example of a configuration ofan electronic apparatus 100 according to a first embodiment. Theelectronic apparatus 100 is an apparatus that produces image data andincludes an imaging lens 110, a solid-state image sensor 200, a digitalsignal processor 120, a frame memory 130, a recording device 140, adisplay device 150, a power supply circuit 160, an operation circuit170, and a bus 180. A mobile apparatus including a digital camera, acamera module, or the like can be assumed as the electronic apparatus100.

The imaging lens 110 condenses light and guides the light to thesolid-state image sensor 200. The solid-state image sensor 200photoelectrically converts light incident from the imaging lens 110 togenerate image data under control of the digital signal processor 120.This solid-state image sensor 200 supplies the image data to the digitalsignal processor 120 via a signal line 209.

The digital signal processor 120 performs predetermined image processingon the image data. The digital signal processor 120 controls thesolid-state image sensor 200 such that the image data is generated inaccordance with an operation of pressing a shutter button or the like.Then, the digital signal processor 120 performs various kinds of imageprocessing on the image data using the frame memory 130 when necessary.The image processing includes demosaicing, white balancing, combining,and the like. The digital signal processor 120 supplies the processedimage data to the recording device 140 via the bus 180 to be recordedtherein. In addition, the digital signal processor 120 causes the imagedata to be displayed on the display device 150 in accordance with anoperation of a user. Note that the digital signal processor 120 is anexample of the image processing unit described in the claim.

The frame memory 130 holds image data (frames). The recording device 140records image data. The display device 150 displays image data. Thepower supply circuit 160 supplies power to circuits installed in theelectronic apparatus 100.

The operation circuit 170 generates an operation signal in accordancewith an operation of a user and supplies the signal to the digitalsignal processor 120. The bus 180 is a common path for exchangingsignals between the digital signal processor 120, the frame memory 130,the recording device 140, the display device 150, the power supplycircuit 160, and the operation circuit 170 with one another.

[Example of Configuration of Solid-State Image Sensor]

FIG. 2 is a block diagram illustrating an example of a configuration ofthe solid-state image sensor 200 according to the first embodiment. Thesolid-state image sensor 200 includes the power supply unit 210, thevertical scanning circuit 230, the pixel array unit 240, the columnsignal processing unit 270, the horizontal scanning circuit 280, and thetiming control unit 285.

The pixel array unit 240 has a plurality of pixel circuits arrayed in atwo-dimensional grid shape. A set of pixel circuits arrayed in apredetermined direction will be referred to as a “row” below, and a setof pixel circuits arrayed in a direction perpendicular to rows will bereferred to as a “column” below. In addition, the number of rows will bedenoted by M (M is an integer) and the number of columns will be denotedby N (N is an integer).

The power supply unit 210 supplies power to the pixel array unit 240.The vertical scanning circuit 230 sequentially selects and drives rowsunder control of the timing control unit 285.

The column signal processing unit 270 performs predetermined signalprocessing on pixel signals from the pixel array unit 240. As the signalprocessing, analog-to-digital (A/D) conversion, and a CDS process areperformed. The column signal processing unit 270 holds processed signalsas pixel data and outputs the signals to the digital signal processor120. Note that the column signal processing unit 270 is an example ofthe signal processing unit described in the claim.

The horizontal scanning circuit 280 controls the column signalprocessing unit 270 and sequentially outputs pixel data of the rowsunder control of the timing control unit 285.

The timing control unit 285 drives the vertical scanning circuit 230,the column signal processing unit 270 and the horizontal scanningcircuit 280 under control of the digital signal processor 120.

Note that, although the frame memory 130 is disposed outside thesolid-state image sensor 200, the frame memory may be disposed insidethe solid-state image sensor 200. In addition, each of circuitsinstalled in the solid-state image sensor 200 may be disposed on thesame chip, or distributed to be disposed on a plurality of stackedchips. In this case, for example, the power supply unit 210, thevertical scanning circuit 230 and the pixel array unit 240 are disposedon one of two stacked chips and the column signal processing unit 270,the horizontal scanning circuit 280 and the timing control unit 285 aredisposed on the other chip.

[Example of Configuration of Pixel Array Unit]

FIG. 3 is a block diagram illustrating an example of a configuration ofthe pixel array unit 240 according to the first embodiment. The pixelarray unit 240 has a plurality of pixel circuits arrayed in atwo-dimensional grid shape. These pixel circuits are classified intoeffective pixel circuits 250 and dummy pixel circuits 260. Each of theeffective pixel circuits 250 is a circuit not shielded from light and apixel signal thereof is read by the column signal processing unit 270.On the other hand, each of the dummy pixel circuits 260 is a circuitshielded from light and no signals thereof are read by the column signalprocessing unit 270.

The effective pixel circuits 250 are disposed in, for example, first toM−1-th rows, and the dummy pixel circuits 260 are disposed in an M-throw. Note that a spot at which the dummy pixel circuits 260 are disposedis not limited to the M-th row. The dummy pixel circuits 260 may bedisposed in, for example, the first row or an N-th column.

In addition, pixel circuits in an m-th (m is an integer from 1 to M) roware connected to a horizontal signal line group 239-m including threesignal lines. Pixel circuits in an n-th (n is an integer from 1 to N)column are connected to a vertical signal line group 219-n includingfive signal lines.

[Example of Configuration of Differential Amplifier Circuit]

FIG. 4 is a circuit diagram illustrating an example of a configurationof a differential amplifier circuit according to the first embodiment.The power supply unit 210 includes P-type transistors 211 and 212, aconstant current source 213, and a bypass control unit 220 for eachcolumn. The bypass control unit 220 includes a bypass transistor 221,resistive elements 222 and 224, and switches 223 and 225.

In addition, each effective pixel circuit 250 includes a transfertransistor 252, a photodiode 253, a reset transistor 254, a floatingdiffusion layer 255, a select transistor 256, and an amplifiertransistor 257.

Meanwhile, each dummy pixel circuit 260 includes a transfer transistor262, a photodiode 263, a reset transistor 264, a floating diffusionlayer 265, a select transistor 266, and an amplifier transistor 267.Note that the graphic symbols indicating capacitors in FIG. 4 representparasitic capacitances of the floating diffusion layers 255 and 265, andthe capacitances are not provided as capacitive components.

The photodiode 253 photoelectrically converts light to generate electriccharges (e.g., electrons). The transfer transistor 252 transfers theelectric charges generated by the photodiode 253 to the floatingdiffusion layer 255 in accordance with a transfer signal TRG_S.

The floating diffusion layer 255 accumulates the electric charges togenerate a voltage corresponding to an amount of electric charges. Thereset transistor 254 sets a voltage of the floating diffusion layer 255to be an initial value in accordance with a reset signal RST_S.

The select transistor 256 opens and closes a path between a signal lineVSL_S and the amplifier transistor 257 in accordance with a selectsignal SEL_S. The amplifier transistor 257 amplifies a voltage of thefloating diffusion layer 255. The amplifier transistor 257 supplies acurrent corresponding to the voltage of the floating diffusion layer 255as a signal current. An output voltage is generated using this signalcurrent and output from the signal line VSL_S. Note that the amplifiertransistor 257 is an example of the signal-side amplifier transistordescribed in the claims.

In addition, a drain of the reset transistor 254 is connected to asignal line VRD_S, and a drain of the select transistor 256 is connectedto the signal line VSL_S.

Configurations of constituent elements included in the dummy pixelcircuit 260 are similar to those of the effective pixel circuit 250.However, a source of the amplifier transistor 267 as well as a source ofthe amplifier transistor 257 is connected to a signal line Vcom. Inaddition, a drain of the reset transistor 264 is connected to the signalline VRD_S to which a reset voltage V_(rst) is applied, and a drain ofthe select transistor 266 is connected to a signal line VSL_D. Inaddition, the transfer transistor, the reset transistor, and the selecttransistor included in the dummy pixel circuit 260 are controlled usinga transfer signal TRG_D, a reset signal RST_D, and a select signalSEL_D. Note that the amplifier transistor 267 is an example of areference-side amplifier transistor described in the claims.

In addition, a gate of the P-type transistor 211 of the power supplyunit 210 is connected to a gate of the P-type transistor 212. A sourceof the P-type transistor 211 is connected to the gate thereof and thesignal line VSL_D, and a drain thereof is connected to a power source ofa power source voltage Vdd. Meanwhile, a source of the P-type transistor212 is connected to the signal line VSL_S, and a drain thereof isconnected to the power source. With this configuration, the P-typetransistor 211 outputs a reference current from the source thereof, andthe P-type transistor 212 outputs a signal current having a value closeto the reference current from the source thereof. The above-describedcircuit is also called a current mirror circuit.

The vertical signal line group 219-n including the signal lines VRD_S,VSL_S, Vcom, VRD_D and VSL_D is provided in each column.

The constant current source 213 performs control to maintain currentsfrom the signal line Vcom to be constant. The constant current source213 is realized by, for example, an N-type transistor to a gate of whicha predetermined bias voltage Vbn is applied.

A differential amplifier circuit that amplifies a pair of differentialinput voltages is configured by the above-described current mirrorcircuit, the amplifier transistors 267 and 257, and the constant currentsource 213. One of the pair of differential input voltages is input tothe amplifier transistor 257 and the other thereof is input to theamplifier transistor 267. Then, output voltages obtained by amplifyingthe differential input voltages are output to the column signalprocessing unit 270 via the signal line VSL_S on the drain side of theamplifier transistor 257.

Such a differential amplifier circuit generally has a higheramplification rate than a source follower circuit that does not performdifferential amplification. For example, a conversion rate of pixels ofa source follower circuit is assumed to be 100 μV/e⁻, output noise of anamplifier transistor thereof is assumed to be 100 μVrms (root meansquare), and noise occurring in A/D conversion is assumed to be 100μVrms. In this configuration, total noise is 141 μVrms, and inputconversion noise is 1.02 e⁻ rms. Meanwhile, a conversion rate of thepixels of the differential amplifier circuit is assumed to be 500 μV/e⁻,output noise of the amplifier transistors is assumed to be 500 μVrms,and noise occurring in A/D conversion is assumed to be 500 μVrms. Inthis configuration, total noise is 510 μVrms, and input-converted noiseis 1.02 e⁻ rms.

In addition, the bypass transistor 221 of the bypass control unit 220is, for example, a P-type MOS transistor, and a gate and a drain thereofare short-circuited (i.e., in diode connection). In addition, a sourceof the bypass transistor 221 is connected to the signal line VSL_S. Notethat the bypass transistor 221 may be an N-type transistor.

One end of each of the resistive elements 222 and 224 is connected tothe drain of the bypass transistor 221. In addition, the other end ofthe resistive elements 222 is connected to a switch 223, and the otherend of the resistive element 224 is connected to the switch 225.Furthermore, resistance values of the resistive elements 222 and 224 aredifferent from each other. Note that the resistive elements 222 and 224are examples of the first and second resistive elements described in theclaim.

The switch 223 opens and closes a path between the resistive element 222and the signal line Vcom in accordance with a switching signal SWP. Theswitch 225 opens and closes a path between the resistive element 224 andthe signal line Vcom in accordance with a switching signal SWD.

The vertical scanning circuit 230 selects any row of the effective pixelcircuits 250 and the row of the dummy pixel circuits 260 at the sametime to drive the circuits using the reset signals, the transfersignals, and the select signals. A pair of an effective pixel circuit250 in the selected row and the dummy pixel circuit 260 in the samecolumn as that of the effective pixel circuit operates as a differentialamplifier circuit to generate a pixel signal. A function of the bypasscontrol unit 220 will be described below in detail.

[Example of Configuration of Column Signal Processing Unit]

FIG. 5 is a block diagram illustrating an example of a configuration ofthe column signal processing unit 270 according to the first embodiment.The column signal processing unit 270 includes a lamp signal generationcircuit 271, N capacitors 272, N capacitors 273, N comparators 274, Ncounters 275, and a data holding unit 276. Each of the capacitors 272,the capacitors 273, the comparators 274, and the counters 275 isprovided in each column.

The lamp signal generation circuit 271 generates a lamp signal having alevel increasing at a constant speed in accordance with control of thetiming control unit 285.

The capacitors 272 hold lamp signals. The capacitors 273 hold pixelsignals coming from corresponding columns. These capacitors realize anautozero function.

The comparators 274 compares lamp signals and pixel signals ofcorresponding columns. These comparators 274 supply the comparisonresults to the counters 275 of the corresponding columns.

The counters 275 count values on the basis of the comparison results ofthe comparators 274. Each of the counters 275 receives a clock signalCLK, and reset signals RSTp and RSTd as an input from the timing controlunit 285. When the reset signal RSTp is input, the counters 275 setcount values to an initial value. Then, the counters 275 increment thecount values in synchronization with the clock signal CLK until a levelof the lamp signal exceeds a level of a pixel signal. Accordingly, aP-phase level is measured.

In addition, when the reset signal RSTd is input, the counters 275reverse the sign of the count values. Then, the counters 275 incrementthe count values in synchronization with the clock signal CLK until thelevel of the lamp signal exceeds the level of the pixel signal.Accordingly, a difference between the P-phase level and a D-phase levelis measured. The counters 275 output data of the difference to the dataholding unit 276 as pixel data. The process of obtaining the differencebetween the P-phase level and the D-phase level is called a CDS process.The capacitors 272 and 273 execute an analog CDS process, and thecounters 275 execute a digital CDS process.

The data holding unit 276 holds N pieces of pixel data. The data holdingunit 276 sequentially outputs the held pieces of the pixel data inaccordance with control of the horizontal scanning circuit 280.

FIG. 6 is a diagram illustrating an example of currents flowing in thedifferential amplifier circuit before limitation according to the firstembodiment. When the P-phase level is to be measured, the verticalscanning circuit 230 performs control such that the switch 223 is in aclosed state using the switching signal SWP and that the switch 225 isin an open state using the switching signal SWD.

Here, a voltage of a node on the source side of the P-type transistor212 is output to the column signal processing unit 270 as an outputvoltage Vo of the differential amplifier circuit. This node will bereferred to as an output node 501 below. In addition, a node of theconstant current source 213 on the amplifier transistor side has acommon-phase voltage. This node will be referred to as a common-phasenode 502 below. The gate of the amplifier transistor 267 receives V_(in)_(_) _(r) that is one of differential input voltages as an input, andthe gate of the amplifier transistor 257 receives V_(in) _(_) _(s) thatis the other one of the differential input voltages as an input. Theinput voltage V_(in) _(_) _(r) is a voltage of the floating diffusionlayer of the dummy pixel circuit 260, and the input voltage V_(in) _(_)_(s) is a voltage of the floating diffusion layer of the effective pixelcircuit 250.

The vertical scanning circuit 230 controls the select transistor 256 ofa selected row and the select transistor 266 included in the dummy pixel260 such that the transistors are in an on-state. Then, the verticalscanning circuit 230 sets the reset transistors 264 and 254 to be in anon-state to initialize the input voltages V_(in) _(_) _(r) and V_(in)_(_) _(s).

The P-type transistor 211 of the current mirror circuit supplies areference current Ir, and the P-type transistor 212 supplies a signalcurrent Is having a value close to the reference current Ir. Thesecurrents are expressed by, for example, the following formulas.Ir=I+ΔI  Formula 1Is=I−ΔI  Formula 1

The reference current Ir and the signal current Is are merged at thecommon-phase node 502, and the sum thereof is controlled by the constantcurrent source 213 to be constant. A current I_(const) caused to flowfrom the common-phase node 502 to a grounded node by the constantcurrent source 213 is expressed using the following formula.I _(const) =Is+Ir  Formula 3

I_(const) of Formula 3 is 2I on the basis of Formulas 1 and 2. Thereference current Ir and the signal current Is are equal immediatelyafter the input voltages V_(in) _(_) _(r) and V_(in) _(_) _(s) areinitialized. For example, if I_(const) is set to be 20 microampere (μA),both the reference current Ir and the signal current Is are 10microampere (μA).

Then, since the effective pixel circuit 250 is not shielded from lightwhile the dummy pixel circuit 260 is shielded from light, the photodiode253 included in the effective pixel circuit 250 generates electriccharges.

The vertical scanning circuit 230 causes the transfer transistor 252included in the effective pixel circuit 250 to be an off-state at thetime of readout of the P-phase level. Thus, electric charges of thephotodiode 253 are not transferred to the floating diffusion layer andthe input voltage V_(in) _(_) _(s) still has the initial value normally.

However, when a very large amount of light is incident, like whenimaging is performed under the sun, the photodiode 253 may generate alarge amount of electric charges, and the electric charges leak into thefloating diffusion layer exceeding a potential of the transfertransistor 252. As a result, there is concern of the output voltage Vo(having the P-phase level) increasing.

In a case in which the output voltage Vo is lower than a limit voltageV_(clip) _(_) _(p) expressed by the following formula, a gate-sourcevoltage of the bypass transistor 221 is lower than a threshold voltage,and thus the bypass transistor 221 is in an off-state.V _(clip) _(_) _(p) =Vc+Rp×Is′+|V _(th)|Vc of the above formula represents a common voltage of the common-phasenode 502, and a unit thereof is, for example, volt (V). Rp represents aresistance value of the resistive element 222, and a unit thereof is,for example, ohm (Ω). Is′ represents a signal current corresponding toV_(clip) _(_) _(p), and a unit thereof is, for example, ampere (A).V_(th) represents a threshold voltage of the bypass transistor 221, anda unit thereof is, for example, volt (V).

In a case in which the bypass transistor 221 is in an off-state (theP-phase level is lower than the limit voltage V_(clip) _(_) _(p)), nocurrent flows in the bypass control unit 220, and the signal current Isflows from the output node 501 to the common-phase node 502 via theamplifier transistor 257.

FIG. 7 is a diagram illustrating an example of currents flowing in thedifferential amplifier circuit after limitation according to the firstembodiment. When the output voltage Vo reaches the limit voltageV_(clip) _(_) _(p), the gate-source voltage of the bypass transistor 221exceeds the threshold voltage and the bypass transistor 221 transitionsto an on-state. Accordingly, the output node 501 and the common-phasenode 502 are connected via the bypass transistor 221 (bypass), and asignal current Is′ flows in the bypass control unit 220. At this time,the P-type transistor 211 supplies Ir′ (=2I−Is′).

Since a current flowing in the constant current source 213 (=Is′+Ir′) isconstant, no current flows in the amplifier transistor 257. Thus, anincrease of the output voltage Vo stops and is fixed to the limitvoltage V_(clip) _(_) _(p) (in other words, clipped).

Then, the vertical scanning circuit 230 causes the switch 223 to be inan open state and the switch 225 to be in a closed state when theD-phase level is read next to the P-phase level. Accordingly, theD-phase level is fixed to a limit voltage V_(clip) _(_) _(d) expressedby the following formula. Note that it is desirable that the limitvoltages V_(clip) _(_) _(p) and V_(clip) _(_) _(d) are equal to or lowerthan an upper limit voltage at which the amplifier transistors operatein a saturation region.V _(clip) _(_) _(d) =Vc+Rd×Is′+|V _(th)|Rd in the above formula represents a resistance value of the resistiveelement 224, and a unit thereof is, for example, ohm (Ω). Since Rp andRd are different values as described above, the D-phase level is clippedat a value different from that of the P-phase level.

Here, a configuration without the bypass control unit 220 is assumed asa comparative example. Also in this comparative example, the photodiode253 generates a large amount of electric charges when very strong lightis incident, and the electric charges may leak into the floatingdiffusion layer, exceeding a potential of the transfer transistor 252.As a result, the output voltage Vo (the P-phase level) increases.

However, since the P-phase level is not limited in the comparativeexample in which the bypass control unit 220 is not provided, theP-phase level can increases up to a value close to the power sourcevoltage Vdd. Although the D-phase level is generated next to the P-phaselevel, a D-phase level having a value close to the power source voltageVdd is likewise generated in an environment of high luminance. If theP-phase level and the D-phase level are equal as described above, adifference thereof approaches “0” in the CDS process, pixel data of ablack level is output in spite of strong incident light. In other words,black dot phenomenon occurs.

On the other hand, in solid-state image sensor 200, since the bypasscontrol unit 220 causes the output node and the common-phase node totake the bypass to limit the P-phase level to the limit voltage V_(clip)_(_) _(p) or lower, the P-phase level and the D-phase level do not havethe same value even if strong light is incident. Accordingly, the blackdot phenomenon can be solved.

In addition, if the limit voltages V_(clip) _(_) _(p) and V_(clip) _(_)_(d) are not set to be an upper limit voltage or lower at which theamplifier transistors operate in a saturation region, there is concernof amplitude of the output voltage Vo significantly increasing whenstrong light is incident. If amplitude of the output voltage Vo islarge, the amplifier transistor 257 may operate in a range of a regionother than the saturation region (a linear region or a cutoff region).In this case, a setting time in which the amplifier transistor 257returns to the saturation region before the next readout starts isnecessary. A frame rate is lowered in accordance with a setting timewhen a plurality of pieces of image data are obtained.

However, in solid-state image sensor 200, the amplitude of the outputvoltage Vo can be suppressed and the amplifier transistor 257 can becaused to operate in the saturation region since the phase levels arelimited to the upper limit voltage of the saturation region or lower.Thus, a setting time is unnecessary and the frame rate can be improvedaccordingly.

Note that, although the solid-state image sensor 200 limits both theD-phase level and the P-phase level, a configuration in which theP-phase level is not limited may be employed in a case in which theP-phase level is limited using an overflow gate or the like. In the casein which the P-phase level is not limited, the resistive elements 224and the switch 225 on the P-phase side are unnecessary.

[Example of Operation of Pixel Circuit]

FIG. 8 is a timing chart showing an example of a driving operation of apixel circuit according to the first embodiment of the presenttechnology. The timing control unit 285 resets a count value CNT of eachof the counters 275 before exposure. In addition, the vertical scanningcircuit 230 sets the select signal SEL_S and the select signal SEL_D ofselected rows to be a high level, and sets the reset signals RST_S andRST_D of the rows to be a high level through a predetermined pulseperiod from a start timing Tr of exposure of the rows.

At the time of reset, the floating diffusion layer is initialized due toa voltage follower function of the differential amplifier circuit, theoutput voltage Vo of the signal line VSL_S of the differential amplifiercircuit has a value close to the reset voltage V_(rst) (a low level).Although voltages of the floating diffusion layers 265 and 255 arelowered due to switch feedthrough when the signal lines RST_S and RST_Dare at a low level, a change in voltages of the signal lines RST_S andRST_D is suppressed due to a common-phase cancellation effect of thedifferential amplifier circuit.

In addition, at a timing Tswp immediately after the timing Tr, thevertical scanning circuit 230 performs control such that the switch 223on the P-phase side is in a closed state by setting the switching signalSWP to a high level. Accordingly, the P-phase level is limited to thelimit voltage V_(clip) _(_) _(p) or lower.

Then, a lamp signal increases through a period from a timing Tps to Tpeafter the timing Tr, and the counters 275 counts the count value CNT_(p)of the P-phase level. That is, the column signal processing unit 270reads the P-phase level. In the case in which very strong light isincident, electric charges leak from the photodiode to the floatingdiffusion layer, the output voltage Vo (the P-phase level) of the signalline VSL_S may continuously increase even after a reset. Since theP-phase level is not limited in the comparative example in which nobypass control unit 220 is provided, the P-phase level may reach a valueclose to the power source voltage Vdd. The thick dotted line in FIG. 8represents an example a change in the output voltage Vo in thecomparative example. If the bypass control unit 220 is provided, theP-phase level is limited as indicated by the solid line in the drawing.

In addition, at a timing Tswd that comes after an exposure time elapsesfrom the reset of the floating diffusion layer, the vertical scanningcircuit 230 sets the transfer signal TRG_S to be a high level throughthe pulse period. Accordingly, electric charges are transferred to thefloating diffusion layer, and an output of the D-phase level starts.Furthermore, the vertical scanning circuit 230 sets the switching signalSWP to be a low level and the switching signal SWD to be a high level,and thereby controls the switch 225 on the D-phase side so as to be in aclosed state. Accordingly, the D-phase level is limited to the limitvoltage V_(clip) _(_) _(d) or lower. In addition, the timing controlunit 285 reverses the sign of the count value of the counter 275 to be−CNT_(p).

Here, a potential difference between the limit voltage V_(clip) _(_)_(p) and the limit voltage V_(clip) _(_) _(d) is set such that, forexample, a count value CNT_(d-p) corresponding to the potentialdifference thereof exceeds full code of pixel data. For example, in acase in which the number of quantization bits of A/D conversion is 12and count values “0” to “4095” are counted, the potential difference isset to exceed a level corresponding to “4095.” In this setting, thesolid-state image sensor 200 can output pixel data with full code(white) when strong light is incident.

The lamp signal increases through the period from a timing Tds after thetiming Tswd to a timing Tde, and the counter 275 counts the count valueCNT_(d-p) corresponding to the difference between the P-phase level andthe D-phase level. Data of this difference is read as pixel data.

The D-phase level is not limited as well in the comparative example inwhich no bypass control unit 220 is provided, and thus the D-phase levelalso increases to a value closed to the power source voltage Vdd. Then,the difference between the P-phase level and the D-phase level becomessubstantially “0,” pixel data having a level close to a black level isoutput. In other words, the black dot phenomenon occurs.

On the other hand, since the bypass control unit 220 limits the P-phaselevel in the solid-state image sensor 200, the black dot phenomenon canbe suppressed. In addition, since the P-phase level and the D-phaselevel are limited to be the upper limit voltage or lower of thesaturation operation region, amplitude of the output voltage Vo can besuppressed, and the amplifier transistor 257 can be set to operate inthe saturation region. Accordingly, a setting time is unnecessary, and aframe rate can be improved accordingly.

FIG. 9 is a flowchart showing an example of an operation of thesolid-state image sensor 200 according to the first embodiment. Thisoperation starts when, for example, an operation for producing imagedata (pressing a shutter button, or the like) is performed.

The vertical scanning circuit 230 selects a row that has not beenselected (Step S901), resets a voltage of the floating diffusion layerof the row (Step S902). In addition, the differential amplifier circuitoutputs the P-phase level limited to the limit voltage V_(clip) _(_)_(p) or lower (Step S903), and then outputs the D-phase level limited tothe limit voltage V_(clip) _(_) _(d) or lower after an exposure timeelapses (Step S904). The column signal processing unit 270 outputs thedifference between the P-phase level and the D-phase level as pixel data(Step S905).

The vertical scanning circuit 230 determines whether a selected row isthe final row (Step S906). In a case in which the row is not the finalrow (No in Step S906), the vertical scanning circuit 230 repeatedlyexecutes the processes from Step S901. On the other hand, in a case inwhich the row is the final row (Yes in Step S906), the vertical scanningcircuit 230 ends an imaging process. Note that, when a plurality ofpieces of image data are produced, the processes of Steps S901 to S906are repeatedly executed until imaging ends.

As described above, according to the first embodiment of the presenttechnology, the bypass control unit 220 connects the output node and thecommon-phase node to flow a signal current therein when the P-phaselevel reaches the limit voltage, the P-phase level can be limited to thelimit voltage or lower even when strong light is incident. Accordingly,the black dot phenomenon caused by the P-phase level and the D-phaselevel having close values and pixel data of a difference thereof being“0” (a black level) can be prevented.

[First modified example]

In the above-described first embodiment, the bypass control unit 220limits the output voltage Vo to two different limit voltages using thetwo resistive elements (222 and 224). However, an output voltage can belimited to two limit voltages with no resistive elements provided. Abypass control unit 220 of a first modified example of the firstembodiment is different from that of the first embodiment in thatlimitation using two limit voltages is realized by the bypass controlunit 220 having no resistive elements.

FIG. 10 is a circuit diagram illustrating an example of a configurationof the differential amplifier circuit according to the first modifiedexample of the first embodiment. The bypass control unit 220 of thefirst modified example is different from that of the first embodiment inthat a bypass transistor 226 is included instead of the resistiveelement 222 and 224.

The bypass transistor 226 is, for example, a P-type MOS transistor, agate and a drain thereof are short-circuited, and a source thereof isconnected to a signal line VSL_S. In addition, a threshold voltage ofthe bypass transistor 226 is different from that of a bypass transistor221. Note that the bypass transistors 221 and 226 are examples of thefirst and second bypass transistors described in the claim. Furthermore,the bypass transistor 226 may be an N-type transistor.

In addition, a switch 223 is connected to a drain of the bypasstransistor 221, and a switch 225 is connected to the drain of the bypasstransistor 226.

Furthermore, if the threshold voltages of the bypass transistors 221 and226 are set to V_(thp) and V_(thd) respectively, limit voltages V_(clip)_(_) _(p) and V_(clip) _(_) _(d) are expressed using the followingformulas.V _(clip) _(_) _(p) =Vc+|V _(thp)|V _(clip) _(_) _(d) =Vc+|V _(thd)|

As described above, according to the first modified example of the firstembodiment of the present technology, the bypass transistors 221 and 226having different threshold voltages limit the threshold voltages, andthus limitation of the two limit voltages can be realized with noresistive elements provided.

[Second Modified Example]

In the above-described first embodiment, the bypass control unit 220limits the output voltage Vo to the two different limit voltages usingthe two resistive elements (222 and 224). However, an output voltage canbe limited to two limit voltages with no resistive elements provided. Abypass control unit 220 according to a second modified example of thefirst embodiment is different from that of the first embodiment in thatlimitation using two limit voltages can be realized by the bypasscontrol unit 220 with no resistive elements provided.

FIG. 11 is a circuit diagram illustrating an example of a configurationof the differential amplifier circuit according to the second modifiedexample of the first embodiment. The bypass control unit 220 accordingto the second modified example is different from that of the firstembodiment in that a selector 227 is included instead of the switch 223,the switch 225, and the resistive elements 222 and 224.

The selector 227 selects one of a power source voltage Vdd, a biasvoltage Vbp, and another bias voltage Vbd in accordance with a selectsignal VSEL and outputs the one to a gate of a bypass transistor 221.The bias voltage Vbp and the bias voltage Vbd have different voltagevalues. In addition, the values of the bias voltage Vbp and the biasvoltage Vbd are set to ones between the power source voltage Vdd and acommon voltage Vc. It is desirable to set these bias voltages to behigher than the common voltage Vc. By setting the bias voltages to behigher than the common voltage Vc, the amplifier transistor 257 canoperate in a saturation operation region.

The vertical scanning circuit 230 causes the bias voltage Vbp to beoutput in a readout period of the P-phase level using a select signalVSEL, and causes the bias voltage Vbd to be output in a readout periodof the D-phase level. In addition, the vertical scanning circuit 230causes the power source voltage Vdd to be output in period other thanthose periods.

Further, limit voltages V_(clip) _(_) _(p) and V_(clip) _(_) _(d) areexpressed using the following formulas.V _(clip) _(_) _(p) =Vc+Vbp−|V _(th)|V _(clip) _(_) _(d) =Vc+Vbd−|V _(th)|

FIG. 12 is a timing chart showing an example of a driving operation of apixel circuit according to the second modified example of the firstembodiment. The dot-and-dash line in the drawing indicates a change of avoltage output by the selector 227.

The vertical scanning circuit 230 changes a voltage output by theselector 227 from the power source voltage Vdd to the bias voltage Vbpusing the select signal VSEL at a timing Tswp before readout of theP-phase level. Then, the vertical scanning circuit 230 changes thevoltage output by the selector 227 to the bias voltage Vbd using theselect signal VSEL at a timing Tswd before readout of the D-phase level.

As described above, according to the second modified example of thefirst embodiment of the present technology, the bypass control unit 220limits an output voltage to two different limit voltages by applying twodifferent bias voltages, and thus limitation using the two limitvoltages can be realized with no resistive elements provided.

<2. Second Embodiment>

Although the dummy pixel circuits 260 are only disposed in the M-th rowin the above-described first embodiment, a distance between theeffective pixel circuit 250 in a row other than M−1-th row and the dummypixel circuit 260 is distant in this disposition. Unevenness incharacteristics of elements installed in a differential amplifiercircuit in which the effective pixel circuits 250 and the dummy pixelcircuits 260 are not in proximity to each other is more significant thanthat in a case in which the effective pixel circuits 250 and the dummypixel circuits 260 are in proximity to each other, which can be a sourceof noise found in image data. For this reason, it is desirable todispose the dummy pixel circuits 260 at positions in proximity to theeffective pixel circuits 250 in terms of a reduction of noise. Asolid-state image sensor 200 of a second embodiment is different fromthat of the first embodiment in that dummy pixel circuits are disposedin proximity to effective pixel circuits.

FIG. 13 is a block diagram illustrating an example of a configuration ofthe solid-state image sensor 200 according to the second embodiment. Thesolid-state image sensor 200 according to the second embodiment isdifferent from that of the first embodiment in that a signal switchingunit 290 is further included.

FIG. 14 is a block diagram illustrating an example of a configuration ofa pixel array unit 240 according to the second embodiment. The pixelarray unit 240 according to the second embodiment has odd-row pixelcircuits 251 disposed in the odd rows and even-row pixel circuits 261disposed in the even rows thereof. All these pixel circuits are notshielded from light.

The odd-row pixel circuits 251 are effective pixel circuits of whichsignals are red by the column signal processing unit 270. On the otherhand, the even-row pixel circuits 261 are dummy pixel circuits of whichno signals are read.

Note that, although the effective pixels and the dummy pixels aredisposed in every other rows in an alternating manner, a configurationis not limited thereto as long as effective pixels are dummy pixels arein proximity to each other. For example, effective pixels may bedisposed in 4k-th and 4k+3-th (k is an integer) rows, and dummy pixelsmay be disposed in 4k+1-th and 4k+2-th rows.

FIG. 15 is a circuit diagram illustrating an example of a configurationof a differential amplifier circuit according to the second embodiment.A power supply unit 210 of the second embodiment is different from thatof the first embodiment in that a differential input limitation unit 300is further included therein.

The differential input limitation unit 300 limits an output voltage of asignal line VSL_E on an even-row pixel circuit 261 (a dummy pixel) sideto a limit voltage or lower. An output voltage of the dummy side (i.e.,one of a pair of differential output voltages) is limited to, forexample, a voltage having the same level as a limit voltage V_(clip)_(_) _(p) with respect to a P-phase level of the other (Vo) of the pairof differential output voltages or lower. The differential inputlimitation unit 300 includes a P-type transistor 301, a resistiveelement 302, and a switch 303.

The P-type transistor is in a diode connection and is inserted between asource of another P-type transistor 211 and the resistive element 302.The switch 303 opens and closes a path connecting the resistive element302 and a constant current source 213 in accordance with a switchingsignal SWR.

In addition, the signal switching unit 290 includes switches 291, 292,293 and 294. The switch 291 switches a connection destination of a drainof a select transistor 266 to one of the P-type transistor 211 and aP-type transistor 212 in accordance with the select signal SWR. Theswitch 292 switches a connection destination of a drain of a selecttransistor 256 to one of the P-type transistor 211 and the P-typetransistor 212 in accordance with the select signal SWR.

The switch 293 switches a connection destination of a drain of a resettransistor 264 to one of a power source of a reset voltage V_(rst) andthe P-type transistor 212 in accordance with the select signal SWR. Theswitch 294 switches a connection destination of a drain of a resettransistor 254 to one of a power source of a reset voltage V_(rst) andthe P-type transistor 212 in accordance with the select signal SWR.

The vertical scanning circuit 230 performs control such that the switch303 enters into a closed state in accordance with the select signal SWRin a case in which the pixels in the odd rows are driven, a connectiondestination of the select transistor 266 directs to the P-typetransistor 211, and a connection destination of the select transistor256 directs to the P-type transistor 212. In addition, the verticalscanning circuit 230 performs control such that a connection destinationof the reset transistor 264 directs to the reset voltage V_(rst) and aconnection destination of the reset transistor 254 directs to the P-typetransistor 212 during driving of the pixels in the odd rows. Thiscontrol makes the connection configuration of the differential amplifiercircuit similar to that of the first embodiment.

On the other hand, the vertical scanning circuit 230 performs controlsuch that the switch 303 enters into an open state in accordance withthe select signal SWR in a case in which the pixels in the even rows aredriven, a connection destination of the select transistor 266 directs tothe P-type transistor 212, and a connection destination of the selecttransistor 256 directs to the P-type transistor 211. In addition, thevertical scanning circuit 230 performs control such that a connectiondestination of the reset transistor 264 directs to the P-type transistor212 and a connection destination of the reset transistor 254 directs tothe reset voltage V_(rst) during driving of the pixels in the even rows.This control makes the connection destinations of the select transistorsand the reset transistors in the odd rows and the connectiondestinations of the select transistors and the reset transistors in theeven rows alternate.

Furthermore, the odd-row pixel circuit 251 is controlled in accordancewith a transfer signal TRG_O, a reset signal RST_O, and a select signalSEL_O, and the even-row pixel circuit 261 is controlled in accordancewith a transfer signal TRG_E, a reset signal RST_E, and a select signalSEL_E.

FIG. 16 is a timing chart showing an example of a driving operation ofthe odd-row pixel circuits 251 according to the second embodiment. Thevertical scanning circuit 230 sets the switch 303 to be in the closedstate using the switching signal SWR set to be a low level to cause theconnection configuration of the differential amplifier circuit to besimilar to that of the first embodiment when the pixels in the odd rowsare driven. Due to the switch 303 set to be in the closed state, a levelof the signal line VSL_E of the dummy pixels (in the even rows) islimited to the limit voltage with respect to the P-phase level of theeffective pixels (in the odd rows) or lower. Limiting the voltage of thesignal line VSL_E on the dummy side described above is because the dummypixels are not shielded from light. The reason for not shielding thedummy pixels from light is that it is difficult to shield only the dummypixels from light in the above-described configuration in which thedummy pixels and the effective pixels are arrayed in an alternatingmanner.

Transmission timings of the transfer signal TRG_O, the reset signalRST_O, and the select signal SEL_O for the odd rows are similar to thoseof the effective pixels of the first embodiment. Transmission timings ofthe transfer signal TRG_O, the reset signal RST_O, and the select signalSEL_O for the even-rows are similar to those of the dummy pixels of thefirst embodiment.

FIG. 17 is a timing chart showing an example of a driving operation ofthe even-row pixel circuits 261 according to the second embodiment. Thevertical scanning circuit 230 causes the connection destinations of theselect transistors and the reset transistors to switch to each otherusing the switching signal SWR set to be a high level. In addition, thevertical scanning circuit 230 sets only the transfer signal TRG_E forthe odd rows to be a high level through a pulse period from a transfertiming Tswd immediately before readout of a D-phase level.

As described above, since the effective pixels and the dummy pixels arearranged in proximity to each other in an alternating manner accordingto the second embodiment of the present technology, unevenness inelement characteristics can be decreased and thus noise can be reducedin comparison to the first embodiment in which there are effectivepixels not in proximity to the dummy pixels.

In addition, the above-described embodiments are examples for embodyingthe present technology, and matters in the embodiments each have acorresponding relationship with disclosure-specific matters in theclaims. Likewise, the matters in the embodiments and thedisclosure-specific matters in the claims denoted by the same names havea corresponding relationship with each other. However, the presenttechnology is not limited to the embodiments, and various modificationsof the embodiments may be embodied in the scope of the presenttechnology without departing from the spirit of the present technology.

Meanwhile, the effects described herein are not necessarily limited andmay be effects described in the present disclosure.

Additionally, the present technology may also be configured as below.

-   (1)

A solid-state image sensor including:

a signal-side amplifier transistor configured to generate an outputvoltage corresponding to a signal current corresponding to one of a pairof differential input voltages by supplying the signal current from anoutput node to a common-phase node;

a reference-side amplifier transistor configured to supply a referencecurrent corresponding to the other one of the pair of differential inputvoltages to the common-phase node;

a constant current source configured to constantly control a sum of thesignal current and the reference current to be merged at thecommon-phase node; and

a bypass control unit configured to connect the output node and thecommon-phase node and supply the signal current having a valuecorresponding to a predetermined limit voltage to the common-phase nodein a case in which the output voltage reaches the limit voltage.

-   (2)

The solid-state image sensor according to (1), further including:

a signal processing unit configured to perform predetermined signalprocessing by reading a signal from an effective pixel circuit among theeffective pixel circuit and a dummy pixel circuit,

in which the signal-side amplifier transistor is disposed in theeffective pixel circuit, and the reference-side amplifier transistor isdisposed in the dummy pixel circuit.

-   (3)

The solid-state image sensor according to (2), in which the dummy pixelcircuit is shielded from light.

-   (4)

The solid-state image sensor according to (2), in which the dummy pixelcircuit is not shielded from light and is disposed in proximity to theeffective pixel circuit.

-   (5)

The solid-state image sensor according to any of (1) to (4), in whichthe bypass control unit includes a bypass transistor having a sourceconnected to the output node.

-   (6)

The solid-state image sensor according to (5),

in which the signal-side amplifier transistor outputs a P-phase level asthe output voltage and then outputs a D-phase level that is differentfrom the P-phase level as the output voltage, and

the limit voltage includes a P-phase limit voltage that limits theP-phase level and a D-phase limit voltage that limits the D-phase level.

-   (7)

The solid-state image sensor according to (6),

in which the bypass control unit further includes first and secondresistive elements connected to the bypass transistor in parallel,

a gate and a drain of the bypass transistor are short-circuited, and

a resistance value of the first resistive element is a valuecorresponding to the P-phase limit voltage, and a resistance value ofthe second resistive element is a value corresponding to the D-phaselimit voltage.

-   (8)

The solid-state image sensor according to (6),

in which the bypass transistor includes first and second bypasstransistors having different threshold voltages,

gates and drains of the first and second bypass transistors areshort-circuited, and

a threshold voltage of the first bypass transistor is a valuecorresponding to the P-phase limit voltage, and a threshold voltage ofthe second bypass transistor is a value corresponding to the D-phaselimit voltage.

-   (9)

The solid-state image sensor according to (6),

in which the bypass control unit further includes a selector configuredto select one of a power source voltage and first and second biasvoltages that are different from each other and supplies the selectedvoltage to a gate of the bypass transistor, and

the first bias voltage is a value corresponding to the P-phase limitvoltage, and the second bias voltage is a value corresponding to theD-phase limit voltage.

-   (10)

An electronic apparatus including:

a signal-side amplifier transistor configured to generate an outputvoltage corresponding to a signal current corresponding to one of a pairof differential input voltages by supplying the signal current from anoutput node to a common-phase node;

a reference-side amplifier transistor configured to supply a referencecurrent corresponding to the other one of the pair of differential inputvoltages to the common-phase node;

a constant current source configured to constantly control a sum of thesignal current and the reference current to be merged at thecommon-phase node;

a bypass control unit configured to connect the output node and thecommon-phase node and supply the signal current having a valuecorresponding to a predetermined limit voltage to the common-phase nodein a case in which the output voltage reaches the limit voltage; and

an image processing unit configured to perform predetermined imageprocessing on image data generated from a signal of the output voltage.

-   (11)

A control method of a solid-state image sensor, the control methodincluding:

an output voltage generation step of generating an output voltage by adifferential amplifier circuit that includes a signal-side amplifiertransistor configured to generate the output voltage corresponding to asignal current corresponding to one of a pair of differential inputvoltages by supplying the signal current from an output node to acommon-phase node, a reference-side amplifier transistor configured tosupply a reference current corresponding to the other one of the pair ofdifferential input voltages to the common-phase node, and a constantcurrent source configured to constantly control a sum of the signalcurrent and the reference current to be merged at the common-phase node;and

a bypass control step of connecting the output node and the common-phasenode and supplying the signal current having a value corresponding to apredetermined limit voltage to the common-phase node in a case in whichthe output voltage reaches the limit voltage.

REFERENCE SIGNS LIST

-   100 electronic apparatus-   110 imaging lens-   120 digital signal processor-   130 frame memory-   140 recording device-   150 display device-   160 power supply circuit-   170 operation circuit-   180 bus-   200 solid-state image sensor-   210 power supply unit-   211, 212, 301 P-type transistor-   213 constant current source-   220 bypass control unit-   221, 226 bypass transistor-   222, 224, 302 resistive element-   223, 225, 291, 292, 293, 294, 303 switch-   227 selector-   230 vertical scanning circuit-   240 pixel array unit-   250 effective pixel circuit-   251 odd-row pixel circuit-   252, 262 transfer transistor-   253, 263 photodiode-   254, 264 reset transistor-   255, 265 floating diffusion layer-   256, 266 select transistor-   257, 267 amplifier transistor-   260 dummy pixel circuit-   261 even-row pixel circuit-   270 column signal processing unit-   271 lamp signal generation circuit-   272, 273 capacitor-   274 comparator-   275 counter-   276 data holding unit-   280 horizontal scanning circuit-   285 timing control unit-   290 signal switching unit-   300 differential input limitation unit

The invention claimed is:
 1. A solid-state image sensor comprising: acurrent mirror circuit including a first transistor and a secondtransistor; a current source circuit; a first pixel circuit coupled to asource or a drain of the first transistor and further coupled to thecurrent source circuit at a first node, the first pixel circuitincluding a first amplifier transistor and a first photodiode; a secondpixel circuit coupled to a source or a drain of the second transistorand further coupled to the first node, the second pixel circuitincluding a second amplifier transistor and a second photodiode; acontrol circuit coupled between the first node and a second node,wherein the second node is coupled between the source or the drain ofthe first transistor and a source or a drain of the first amplifiertransistor, wherein the second node is configured to output a pixelsignal; a ramp signal generation circuit configured to output a rampsignal; and a comparator configured to compare the ramp signal and thepixel signal, wherein a gate of the first amplifier transistor isconfigured to receive a first one of a pair of differential inputvoltages and a gate of the second amplifier transistor is configured toreceive a second one of the pair of differential input voltages.
 2. Thesolid-state image sensor according to claim 1, wherein the controlcircuit includes a third transistor, wherein a gate of the thirdtransistor is arranged to receive a first voltage.
 3. The solid-stateimage sensor according to claim 2, wherein the first voltage isdifferent from a second voltage supplied to the first transistor.
 4. Thesolid-state image sensor according to claim 2, wherein the thirdtransistor is configured to receive a first voltage or a second voltageselectively via a selector.
 5. The solid-state image sensor according toclaim 4, wherein the third transistor is configured to receive the firstvoltage, the second voltage or a third voltage selectively via theselector.
 6. The solid-state image sensor according to claim 1, whereinthe solid-state image sensor is a differential amplification-typesolid-state image sensor.
 7. The solid-state image sensor according toclaim 1, further comprising a first imaging pixel circuit and a firstdummy pixel circuit, wherein the first imaging pixel circuit includesthe first pixel circuit and the first dummy pixel circuit includes thesecond pixel circuit.
 8. The solid-state image sensor according to claim6, further comprising a shielding material arranged to shield the firstdummy pixel circuit from incident light.
 9. The solid-state image sensoraccording to claim 6, wherein the first dummy pixel circuit is notshielded from incident light, and wherein the first dummy pixel circuitis disposed in proximity to the first imaging pixel circuit.
 10. Thesolid-state image sensor according to claim 1, wherein a gate of thefirst transistor is coupled to a gate of the second transistor.
 11. Thesolid-state image sensor according to claim 1, further comprising acounter configured to count a value based on a comparison result of thecomparator.
 12. The solid-state image sensor according to claim 1,wherein the first pixel circuit includes a first reset transistor andthe second pixel circuit includes a second reset transistor.
 13. Thesolid-state image sensor according to claim 12, wherein a drain or asource of the first reset transistor is coupled to a power sourcevoltage via the first transistor and a drain or a source of the secondreset transistor is coupled to a reset voltage having a value that isdifferent from the power source voltage.